This invention relates to circuit components mounted on circuit boards by solder column interconnects or arrays, and more particularly, the support of circuit components having column grid arrays.
Solder column interconnects or arrays are used to interconnect circuit packages to circuit boards, most typically large ceramic integrated circuit packages. One such package is the column grid array (CGA) integrated circuit package that has a ceramic substrate with an array of solder columns that extend out from it, typically from the bottom surface. The solder columns are attached at one end to connection pads or locations on the ceramic substrate. The solder columns are sufficiently tall so that when the circuit package is placed on a circuit board, the solder columns can accommodate the difference in thermal expansion between the ceramic integrated circuit package and the printed circuit board. The solder columns are soldered to respective pads on the circuit board using known techniques, such as a convection reflow solder process.
One problem with solder column arrays is that the solder columns do not withstand compressive force well. The solder columns in the solder column arrays are typically made of a 90%/10% Pb/Sn solder, making them soft. Moreover, the individual solder columns are very thin. Consequently, if any significant amount of compressive force is applied to the circuit package, such as might be applied by a cooling solution such as a heat sink or fan, the resulting weight on the circuit package may cause the solder column array to compress, particularly over time, which may compromise reliability. In this regard, loads in excess of about 10 to 20 grams per column exert sufficient compressive force so that reliability may be compromised. Since CGA integrated circuit packages are being increasingly used for high power integrated circuits, the cooling solution required often has considerable mass. It is not unusual for the heat sink or cooling solution used with such high power integrated circuits to exceed one pound. When such large cooling solutions are exposed to shock and vibration that is encountered at the system level, it is not uncommon to have thirty to forty pounds of force applied to the top of the integrated package. Such high loading can cause the solder columns to bend and deform.
In one aspect of the present invention, a support assembly useful for supporting an integrated circuit package having an array of solder columns extending to a circuit board when the integrated circuit package is mounted on the circuit board is provided. The support assembly includes a support means for supporting the integrated circuit package and the support means has a ramped surface. Also included is a biasing means associated with the support means for coupling the ramped surface to the integrated circuit package such that the support means resists downward movement of the integrated circuit package.
In another aspect of the present invention, a support assembly useful for supporting an integrated circuit package having an array of solder columns extending to a circuit board when the integrated circuit package is mounted on the circuit board is provided. The support assembly includes a support member supporting the integrated circuit package and the support member has a ramped surface. Also included is a cooperating support member having a cooperating ramped surface cooperating with the ramped surface of the support member. Additionally included is a biasing member associated with the first and second support members to bias the first and second ramped surfaces together to adjust a height of the combined first and second support members to contact the integrated circuit package.
In yet another aspect of the present invention a method useful for supporting an integrated circuit package mounted on the circuit board by an array of solder columns extending between the integrated circuit package and the circuit board is provided. The method includes locating a support member having a ramped surface in a position to support the integrated circuit package. The method also includes biasing the support member to retain the support member in supporting relationship with the integrated circuit package and enabling the support member to resist a downward force on the integrated circuit package.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.